39 - MCB 142 Professor Georjana Barnes Lecture 39 ASUC...

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11/26/07 Lecture 39 ASUC Lecture Notes Online (formerly Black Lightning) is the only authorized note-taking service at UC Berkeley. Please do not share, copy or illegally distribute these notes. Our non-profit, student-run program depends on your individual subscription for its continued existence. These notes are copyrighted by the University of California and are for your personal use only. Sharing or copying these notes is illegal and could end note taking for this course ANNOUNCEMENTS Office hours today: 1-2PM, 301 Barker Wednesday: 12-1, 301 Barker REVIEW Today we’re going to look at the influences on gene expression in the genome of Drosophila to see how an embryo turns into male or female. Male and females differ in appearance, behavior, and the types of germ line development that they undergo (males produce sperm, females produce eggs). If you had Bio1A, you probably did a Drosophila experiment and saw the differences between the two genders. What we’re going to do today is see how genetic analysis of mutant flies shows the difference in the chromosomal make-up. There are two points we’re going to consider – the content of chromosomes in males and females and how that difference affects the outcome of being male or female. Specifically, we’re going to look at the X:A ratio to see how that factor influences how the fly behaves, looks, and what kind of germ line develops and also the influence of the X:A ratio on viability. An analysis of mutant flies showed researchers that there was a difference in the biology of the fly depending on its X:A ratio. Analysis of mutations in the genome showed that they affected males differently than they did females. SEX DETERMINATION IN DROSOPHILA X:A Ratio First I want to explain how chromosomal makeup affects whether a fly turns out to be male or female. For male and females, they both have two autosomes. It’s the ratio of X:A (X chromosomes: autosomes) that is measured when determining whether a fly will be male or female. So in females, they have two X and two A so the ratio is 1. If you’re male and you have one X, then your ratio is ½. When Drosophila geneticists looked at mutants now, they saw different situations depending on the X:A ratio. So you can generate flies that have only X and no A, in which case your ratio is ½ and you turn out to be male. But this male is sterile because there are certain genes on the Y chromosome that specify germ line developmental events. You can also make a fly with XXY so then the X:A ratio is 1 and those flies are female and fertile. Then it can get whacky. When you start increasing the number of A until you have XXX and three A, your ratio is 1 and then you’re female. If you have XYY, then your X:A ratio is 0.33, which allows the embryo to develop as male. If you have XXY, then your ratio is 0.66, and the resulting fly has traits of both females and males; they are called intersex. So the flies are using their numbers of
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This note was uploaded on 04/04/2008 for the course MCB 142 taught by Professor Slatkin during the Fall '08 term at Berkeley.

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39 - MCB 142 Professor Georjana Barnes Lecture 39 ASUC...

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